I always open up with thunder II (cast it as tank running to the boss, Thu II initial aggro is very low u wont pull boss if tank open with shield lop) then I follow up with Fire 3 then Raging strike > fire 1 spam, then closing with double flare. (do first flare w/ swift cast to ensure it got raging strike effect. raging strike is usually gone when i hard cast 2nd flare.

I dont use thunder for damage (I use it for a chance Thunder proc ) so i dont cast it during raging strike.